KR100806891B1 - a thin film transistor for a liquid crystal display - Google Patents

Abstract

The thin film transistor substrate for a liquid crystal display according to the present invention includes a gate line connected to a gate line and a gate line in a horizontal direction, and a gate wiring for transmitting a gate signal to a pixel row and a wiring for a storage capacitor in a horizontal direction. Formed. On the gate insulating film covering them, a drain is formed on the semiconductor layer, the data line crossing the gate line, and the source electrode connected to the data line and formed on the semiconductor layer facing the source electrode centered on the source electrode and the gate electrode. A data wiring including an electrode is formed. Here, it includes a conductive pattern for a storage capacitor, which is formed of the same layer as the data wiring and extends from the drain electrode and overlaps with the storage capacitor wiring. An insulating film covering the semiconductor layer and having a contact hole exposing the drain electrode is formed on the substrate, and a pixel electrode is formed on the insulating film. In particular, the gate lines are arranged to completely overlap with the pixel electrodes of the adjacent pixel rows. At this time, in the transmissive mode and the reflective transmissive combined mode, it is preferable to provide the storage capacitor wiring between the pixel electrodes of adjacent pixel rows.

Declination, Black Matrix, Kickback Voltage, Flicker, Holding Capacitance

Description

Thin film transistor substrate for a liquid crystal display device

1 is a layout view illustrating a structure of a thin film transistor substrate for a liquid crystal display device in a reflective mode according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II 'of FIG. 1.

3 is a layout view illustrating a structure of a thin film transistor substrate for a liquid crystal display device in a transmissive mode according to an exemplary embodiment of the present invention.

4 is a cross-sectional view taken along the line IV-IV 'of FIG. 3.

5 is a layout view illustrating a structure of a thin film transistor substrate for a liquid crystal display device in a reflective transmissive composite mode according to an exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view taken along the line VI-VI 'of FIG. 5.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thin film transistor substrates for liquid crystal display devices, and more particularly, to thin film transistor substrates used in liquid crystal display devices of reflective, transmissive, and reflective transmission complex mode.                         

The liquid crystal display is one of the most widely used flat panel display devices. The liquid crystal display includes two substrates on which electrodes are formed and a liquid crystal layer interposed therebetween, and rearranges the liquid crystal molecules of the liquid crystal layer by applying a voltage to the electrode. By controlling the amount of light transmitted.

Such a liquid crystal display has a transmissive mode in which light emitted by a backlight, which is a light source, is transmitted through a liquid crystal panel to display an image, and a reflective mode in which external light including natural light is reflected on a reflective film of a liquid crystal panel to display an image. It can be divided into the reflection transmission complex mode in which these two modes are superimposed.

In this case, the liquid crystal display of the reflective or reflective transmissive composite mode overlaps the pixel electrodes formed in the pixel region with each other to overlap the wirings defining the pixel region, and is formed on the thin film transistor to maximize the reflectance. It is common to maximize the area.

On the other hand, in the liquid crystal display of the transmissive mode, in order to block light leaking from the backlight between neighboring pixel regions, a black matrix (i. A black matrix (BM) is formed in which a transparent pixel electrode is connected to data lines such as the liquid crystal display of the reflective and reflective transmission mode to form a black matrix with a minimum width to prevent the aperture ratio from being reduced. And overlapping with the gate wiring and extending to the upper portion of the thin film transistor.

However, the following problem occurs in the structure in which the pixel electrode overlaps the data wiring, the gate wiring, and the thin film transistor.

A transverse electric field is formed between the gate electrode and the pixel electrode formed between the pixel electrodes of neighboring pixel regions, and due to the transverse electric field, the arrangement of the liquid crystal molecules is inverted at the edge of the pixel electrode, so that the disclination is performed. Occurs. The disclination line lies inward from the end of the pixel electrode in proportion to the voltage difference between the pixel electrode and the gate wiring.

In order to prevent this, in the related art, the disclination line is designed to extend on the overlapping width of the gate line and the pixel electrode, but in practice, there is a problem in that the disclination line varies depending on the process conditions.

In addition, in the case where the thin film transistor is turned on, the voltage applied to the liquid crystal capacitor and the storage capacitor should continue to be maintained even after the thin film transistor is turned off, but parasitics between the gate electrode and the source electrode of the thin film transistor Because of the capacitance, the voltage applied to the pixel electrode causes distortion. At this time, the parasitic capacitance generated due to the overlap between the gate wiring and the pixel electrode is further added, so that the distortion of the voltage applied to the pixel electrode is more severe. In this case, the distorted voltage is referred to as a kickback voltage, which appears when the gate wiring is changed from an ON voltage to an OFF voltage. The magnitude of the distorted voltage may be expressed by Equation 1 below.

dVp = dVg * (Cgs + Cgs ') / (Cgs + Cgs' + Clc + Cst + ...)

Here, Clc is a liquid crystal capacitance, Cgs is a parasitic capacitance between the gate electrode and the source electrode, and Cgs' is a parasitic capacitance generated due to overlap between the wiring and the pixel electrode. dVg is the difference between the on voltage and the off voltage.

The kickback voltage acts to lower the pixel voltage, which intensifies the flicker phenomenon in which the screen flickers in a liquid crystal display device displaying an image through oscillation driving. In addition, in the divisional exposure method in which wiring is formed by a photolithography process in which a substrate is divided into a plurality of areas and exposed, a stitch phenomenon in which brightness is unevenly generated for each divided area occurs.

An object of the present invention is to provide a thin film transistor substrate capable of minimizing the flicker phenomenon and the stitch phenomenon in the liquid crystal display device of the reflection type, transmissive mode, and reflective transmission mode.

In the thin film transistor substrate according to the present invention, the gate lines completely overlap with the pixel electrodes of adjacent pixel rows.

More specifically, the thin film transistor substrate for a liquid crystal display according to the present invention includes a gate wiring including a gate line formed in a horizontal direction and transmitting a scan signal and a gate electrode connected to the gate line, and for a storage capacitor in a horizontal direction. Wiring is formed. On the gate insulating film covering these, a semiconductor layer overlapping with the gate electrode, a source electrode connected to the data line and the data line insulated from and intersecting the gate wiring and the storage capacitor wiring, and formed on the semiconductor layer, gate A data line is formed including a drain electrode formed on the semiconductor layer facing the source electrode with respect to the electrode. It may include a conductive capacitor pattern formed from the same layer as the data wiring and extending from the drain electrode and overlapping the wiring for the storage capacitor. The pixel electrode is formed on the insulating film which covers these on the board | substrate, and this pixel electrode fully overlaps the gate line which transmits a scanning signal to the pixel of the adjacent pixel row.

On the other hand, in the thin film transistor substrate for liquid crystal display devices of the transmissive mode and the reflective transmissive mode including a backlight, it is preferable to form the storage capacitor wiring between the pixel electrodes of adjacent pixel rows.

Next, a thin film transistor substrate for a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings so that a person skilled in the art may easily implement the present invention.

First, the structure of a thin film transistor substrate for a liquid crystal display device according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

1 is a layout view of a thin film transistor substrate for a reflective liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view of the thin film transistor substrate illustrated in FIG. 1 taken along the line II-II ′.

The gate wiring and the storage capacitor wiring are formed to extend in the horizontal direction on the insulating substrate 10.

The gate wiring includes a gate line 22 extending in a horizontal direction and transmitting a scan signal, and a gate electrode 26 of a thin film transistor that is part of the gate line 22. The gate line 22 receives a scan signal from the outside. It may include a gate pad for transferring to.

The storage capacitor wiring 28 extends in the horizontal direction and overlaps the pixel electrode 92 or the storage capacitor conductor 64 to be described later by receiving a voltage such as a common electrode voltage input to the common electrode of the upper plate from the outside. This results in a sustain capacitor which improves the charge retention capability of the pixel.

The gate wirings 22 and 26 and the storage capacitor wiring 28 may be formed of a single layer made of aluminum or an aluminum alloy, but may be formed of a conductive film of chromium or molybdenum or molybdenum alloy or tantalum or titanium having excellent contact properties with other materials. It may include.

On the substrate 10, a gate insulating film 30 made of silicon nitride (SiN _x ) covers the gate wirings 22 and 26 and the storage capacitor wiring 28.

A semiconductor layer 40 made of a semiconductor such as amorphous silicon is formed on the gate insulating layer 30 of the gate electrode 26, and n + having a high concentration of silicide or n-type impurities is formed on the semiconductor layer 40. Resistive contact layers 55 and 56 made of a material such as hydrogenated amorphous silicon are formed, respectively.

On the resistive contact layers 55 and 56 and the gate insulating layer 30, data wirings including a conductive film made of a low resistance conductive material such as aluminum or silver are formed. The data line is formed in a vertical direction and includes a data line 62 intersecting the gate line 22, a source electrode 65 connected to the data line 62, and extending to an upper portion of the resistance contact layer 55. And a drain electrode 66 which is separated from the 65 and formed on the ohmic contact layer 56 opposite the source electrode 65 with respect to the gate electrode 26. In addition, the data line includes a conductive capacitor pattern 64 extending from the drain electrode 66 and overlapping with the storage capacitor line 28, and is connected to one end of the data line 62 and is connected from the outside. May include a data pad configured to receive an image signal and transmit the image signal to the data line 62.

An organic insulating layer 80 made of an organic material having excellent planarization characteristics is formed on the data lines 62, 64, 65, and 66 and the semiconductor layer 40 which is not covered. In this case, an upper surface of the organic insulating layer 80 is formed in a concave-convex pattern in order to maximize reflection efficiency in the liquid crystal display of the reflective mode.

A protective film made of silicon nitride or the like may be further formed below the organic insulating layer 80.

The organic insulating film 80 is formed with contact holes 76 exposing the conductive pattern conductor 64 for the storage capacitor extending from the drain electrode 66, which together with the contact hole and gate insulating film 30 exposing the data pads. And a contact hole exposing the gate pad.

The upper portion of the organic insulating layer 80 is connected to the drain electrode 66 through the contact hole 76 and used as the pixel electrode of the pixel, and has high reflectance such as aluminum or aluminum alloy, silver or silver alloy, molybdenum or molybdenum alloy, etc. The reflection film 921 made of a conductive film is formed.

 In this case, in the thin film transistor substrate according to the exemplary embodiment of the present invention, the gate lines 22 and 26 are disposed to completely overlap the pixel electrodes 921 formed in the adjacent pixel rows. In this way, the transverse electric field generated between the gate wirings 22 and 26 and the pixel electrode 921 can be minimized, so that the arrangement of the liquid crystal molecules can be reversed, thereby minimizing the discretization.

In addition, since the gate wirings 22 and 26 do not overlap with the pixel electrodes of the pixel rows that drive and transmit the scan signals, the kickback voltage is almost caused only by the parasitic capacitance Cgs between the gate electrode and the source electrode of the thin film transistor. . The size may be expressed as in Equation 2.

dVp = dVg * (Cgs) / (Cgs + Cgs' + Clc + Cst + ...)

This may minimize flickering in which an image flickers.

In addition, even when the divisional exposure method in which a photolithography process is performed by dividing a substrate into a plurality of regions in order to manufacture the thin film transistor according to the exemplary embodiment of the present invention, a gate line transfers a scan signal to drive a pixel row. Since the pixels do not overlap with the pixel electrodes but completely overlap with the pixel electrodes of neighboring pixel rows, the stitch phenomenon in which brightness is unevenly generated for each divided region due to misalignment of wirings at the boundary between the divided regions can be eliminated.                     

On the other hand, in the thin film transistor substrate for the liquid crystal display device in the reflective mode, only the insulating film and the substrate exist between the pixel electrodes of the neighboring pixel rows because the gate wiring is completely overlapped with the pixel electrodes of the neighboring pixel rows. Accordingly, in the transmissive and reflective transmissive modes with backlight, light from the backlight may pass through and leak between pixel electrodes of adjacent pixel rows. In order to prevent this, the opposite substrate facing the lower substrate 10 is prevented. A black matrix is formed between the pixel regions of the. In this case, the black matrix is preferably formed to have a wide width in consideration of misalignment of the two substrates. However, since the aperture ratio is reduced, the width of the black matrix is minimized and the storage capacitor wiring is formed between the pixel electrodes of adjacent pixel rows. can do. The structure of the thin film transistor substrate for a liquid crystal display of the transmissive mode according to the exemplary embodiment of the present invention will be described with reference to the drawings.

3 is a layout view of a thin film transistor substrate for a transmissive liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a cross-sectional view of the thin film transistor substrate illustrated in FIG. 3 taken along line IV-IV ′.

Most of the structure is the same as the embodiment of the reflective mode as shown in Figs. However, the storage capacitor wiring 28 is formed between the pixel electrodes 922 of adjacent pixel rows. Here, the pixel electrode 922 is made of a transparent conductive material such as ITO and IZO.

Meanwhile, as described above, the structure in which the gate line overlaps with the pixel electrodes of the neighboring pixel rows may be applied to the reflection-transmission hybrid mode having both the reflection mode and the transmission mode, and will be described in detail with reference to the accompanying drawings.

5 is a layout view of a thin film transistor substrate for a reflective transmissive liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 6 is a cross-sectional view of the thin film transistor substrate illustrated in FIG. 5 taken along the line VI-VI ′.

As shown in FIGS. 5 and 6, as in the reflective or transmissive mode, the gate lines 22 and 26 are formed to completely overlap the pixel electrodes 921 and 922 formed in the adjacent pixel rows. In addition, the storage capacitor wiring 28 is formed between the pixel electrodes 921 and 922 of adjacent pixel rows.

However, the pixel electrode includes a reflective film 921 made of a conductive material having a reflectance and a transparent film 922 made of a transparent conductive material, wherein the reflective film 921 has an opening that exposes a part of the transparent film 922.

The transparent film 922 is formed of a conductive material such as ITO or IZO, and the reflective film 921 is preferably made of a conductive material having a high reflectance such as aluminum or an aluminum alloy, silver or silver alloy, molybdenum or molybdenum alloy.

As described above, in the present invention, the gate line overlaps the pixel electrodes of the adjacent pixel rows, thereby minimizing the transverse electric field formed at the edges of the pixel electrodes, thereby reducing the discretization of the arrangement of the liquid crystal molecules. This also minimizes the flicker that causes images to flicker by minimizing the parasitic capacitance that causes kickback voltage. In addition, in the thin film transistor substrate of the transmissive type and the reflective transmissive combined mode, the black matrix width can be reduced by forming the storage capacitor wiring between the pixel electrodes of adjacent pixel rows, thereby maximizing the aperture ratio.

Claims (6)

Insulation board, A gate wiring formed on the insulating substrate in a horizontal direction and including a gate line transferring a scan signal and a gate electrode connected to the gate line; A storage capacitor wiring formed on the insulating substrate in a horizontal direction; A semiconductor layer overlapping the gate electrode; A data line intersecting and insulated from the gate line and the storage capacitor line and a semiconductor layer connected to the data line and facing the source electrode with respect to the source electrode formed on the semiconductor layer and the gate electrode; A data line including a drain electrode formed on the upper portion, A pixel electrode in which the gate line transferring the scan signal is completely overlapped with a pixel in a neighboring pixel row Including, And the data line includes a conductor pattern for a storage capacitor that extends from the drain electrode and overlaps with the storage capacitor line. In claim 1, The thin film transistor substrate for liquid crystal display device, wherein the storage capacitor wiring is formed between pixel electrodes of adjacent pixel rows. delete In claim 2, The pixel electrode is a thin film transistor substrate for a liquid crystal display device consisting of a conductive film having a reflectance. In claim 2, The pixel electrode is a thin film transistor substrate for a liquid crystal display device made of a transparent conductive material. In claim 2, The pixel electrode includes a reflective film made of a conductive material having a reflectance and a transparent film made of a transparent conductive material, and the reflective film has an opening that exposes a portion of the transparent film.

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